There have been proposals of digital image enlargement for displaying one image on media of different display sizes or resolutions. Image enlargement is carried out by increasing the interval between pixels contained in an original image (hereinafter called “original pixels”) and generating new pixels between original pixels. A signal value for a new pixel can be determined by interpolation of signal values associated with original pixels surrounding the new pixel. This enables the same image as the original image to be displayed on a display media having a larger display size or a higher resolution. As image display devices with high resolution (video display devices like computers or televisions) have become popular in these years, image enlargement for display media is increasingly important.
As examples of image enlargement techniques, NPL 1 describes nearest neighbor interpolation (also known as nearest neighbor method), bi-linear interpolation (also known as bi-linear method or linear interpolation), and bi-cubic interpolation (also known as cubic convolution interpolation).
Nearest neighbor interpolation is a process in which the signal value of the original pixel closest to a pixel to be newly generated (hereinafter, referred to as “interpolated pixel”) is adopted as the signal value for the interpolated pixel.
Bi-linear interpolation is a process in which a weighted mean of signal values of four original pixels surrounding an interpolated pixel is determined as the signal value for the interpolated pixel.
Bi-cubic interpolation is a process in which the signal value for an interpolated pixel is determined using a cubic equation adapted to the signal values of 16 original pixels that surround the interpolated pixel.